ON October 24, 1632, four days after the birth of Sir Christopher Wren at East Knoyle, Wiltshire, the tercentenary of which has just been celebrated, Antony van Leeuwenhoek, the eminent Dutch naturalist who has been called the “Father of Protozoology and Bacteriology” was born at Delft. Both Wren and Leeuwenhoek were long associated with the Royal Society in its early days, and both lived to extreme old age; Leeuwenhoek outliving Wren by six months and dying at Delft on August 26, 1723, being then aged—as his epitaph says—“90 years, 10 months, and 2 days”. But the careers of these two distinguished men followed very different lines; for while Wren was first a professor of astronomy and then a great architect, Leeuwenhoek began his life as a draper and haberdasher with few advantages of education, and his fame came through his lifelong devotion to microscopical studies. The son of a basket maker, he was sent to a school at Warmond, near Leyden, and at sixteen was an apprentice in Amsterdam. At the age of twenty-two years he married and set up in business for himself in his native town, and for thirty-nine years was “Chamberlain of the Council-Chamber of the Worshipful Sheriffs of Delft”. He was also a surveyor and wine gauger. When he began his work with his simple microscopes is not known, but at the age of forty-one years he addressed the first of his many letters to the Royal Society, then eager to get into touch with all men working for “the promotion of natural knowledge”, and it was through these letters he became famous. He was made a fellow of the Royal Society in 1679 (1680 N.S.), a correspondent of the Paris Academy of Sciences in 1699, and in 1716 the University of Louvain presented him with a medal. At his death at Delft in 1723 he was buried in the Old Church, in which his daughter Maria, in 1739, erected a monument to his memory.